All recommended methods avoid downloading BOOTMGR from untrusted third parties. They rely on Microsoft's own tools, your original Windows 7 installation media, or legitimate system repair discs.
D: cd boot bootsect /nt60 SYS /mbr
Type select disk X (replace with the disk number containing Windows, usually 0). Type list partition to see the partitions on that drive. windows 7 bootmgr download